The truth about the Resistance and the Aubracs.

For your information, the "lettres de cachet" were letters signed by the king of France, countersigned by one of his ministers, and closed with the royal seal (the "cachet"). They contained orders directly from the king, often to allow imprisonment without trial and without an opportunity of defense to imprisonment, confinement in a convent or a hospital, transportation to the colonies, or expulsion to another part of the realm of France. It was a sort of direct justice, when the king could decide without heeding the laws, and even contrary to the laws (that is say... absolutism at its best).
The "lettres de petit cachet", however, were signed simply by a secretary of state for the king; they bore merely the imprint of the king's privy seal, and were entirely exempt from the control of the chancellor. They were employed by the police in dealing with prostitutes, and on their authority lunatics were shut up in hospitals and sometimes in prisons. They were also often used by heads of families as a means of correction, for example, for protecting the family honor from the disorderly or criminal conduct of sons. In the XVIIIth century it is certain that the letters were often issued blank, i.e. without containing the name of the person against whom they were directed; the recipient, or mandatary, would fill in the name in order to make the letter effective.
The "lettres de cachet" were aptly abolished during the French Revolution by the Constituent Assembly as a symbol of monarchism and its abuses.

It seems to me that the connection between feudal direct justice and letters of denunciation sent by mail during WWII is a very loose one, don't you think?

But at least you are right about the fact that thousands of anonymous letters were sent during WWII, out of hatred, jealousy, pettiness, greed... you name it. In this country this activity was called a "national sport" (not a pastime ). Now, I remember a historian saying in a documentary about denouncement during the Nazi Occupation: "Had the people been aware of the consequences of their acts, I don't think they would have sent all those letters in the first place". As for me, I don't believe too much in human kindness, so I don't know to what extent this remark is true.
But were all the senders collaborators? Frankly, I don't know how to answer this question. Given that most of letters of denunciation dealt with petty family matters and not with the French Jews (that's why Nazi authorities didn't bother to read them all), I don't know how we should qualify their senders.
The other interesting thing would be to find out what was the situation in other occupied countries. Not to mention the dictatorships (fascist Italy, the USSR and Nazi Germany) where denouncement was an integral part of state policy.

I doubt that the French are a special kind from that point of view. See what happens these days with the WWW. There was never so much finger-pointing, bashing and denouncement before the creation of online networks. Anonymity does wonders.

If you care to read a little, here is an interesting document (not too long): http://historytodaymagazine.blogspot.com/2008/12/international-colloqu ium-sheds-new.html and more on the very same subject at http://www.telegraph.co.uk/news/worldnews/europe/france/3543112/Petty- disputes-led-to-Nazi-denunciation-in-WWII-France.html.
Henri-Georges Clouzot had captured the very essence of denouncement in his film "Le Corbeau", which was hated by both the Nazis and the French Resistance after the Liberation. If you like old movies, you should not miss this one: http://www.imdb.com/title/tt0035753/